In order to be successful on the market, the products of household glass category, as e.g. beverages glasses, candlesticks and vases made of crystal glass must satisfy the claims of the widest consumer area from the point of view of the acceptable price, of aesthetic and utility properties. The costs of the used material, the actual cost of necessary manufacturing apparatus and of the necessary moulds have the decisive influence on the price of such product. From the point of view of price, it is useful to use the barium crystal glass which price is multiple lower than the price of the lead crystal glass. As far as the beverage glass is concerned, also the conviction of some consumers (though ungrounded) of the health harmfulness of the lead crystal glass due to the possible getting lose of lead from the flask into the beverage speaks for the benefit of barium crystal glass. From the aesthetic point of view, the customers prefer the household glass, the stem of which makes with the flask a compact whole because it evokes the impression that the product was made by the traditional hand-made blowing mode. On the contrary, the household glass, the stem of which does not make a compact whole with the flask, customers identify as the mass production on machines that is inevitable to meet market needs on quantity and price of the household glass. Also from the point of view of practical properties of use, representing above all the simple keeping clear and the long service life of the beverage glass, customers prefer glasses, the stem of which makes with the flask a compact whole.
The household glass with a stem is being manufactured with a pressed stem or with a drawn one. The drawn stem is being manufactured as a separate part. The stem will be then welded to the cup that was manufactured on the blowing apparatus in the glass-blowing mould. From the point of view of price, it is advantageous that the cup is manufactured on the relatively simple automatic blowing apparatus, i.e. the actual cost for the manufacturing apparatus and moulds, the operation and maintenance costs of such machine are relatively low. With regard to the fact that the cup making is carried only in the glass-blowing mould, the quality of its outer surface is very high. But the disadvantage of the barium crystal glass consists in the fact, that high internal stresses occur in the products made of it during the cooling down, the elimination of which needs the use of further technological operations. This disadvantageous property of the barium crystal glass is growing in welding the flask to the pressed stem that are heated-up to the unequal temperature, in consequence of that extraordinary high internal stresses occur on the welding spot. These facts cause problems with the cracking of glass products during the manufacturing, and in consequence of residual internal stress, these problems occur also at customers. Besides the fact that it can come to spontaneous rupture of the glass product, mainly the cleaning of the beverage glass in automatic dish-washing machines is dangerous. From the point of view of cleanness maintaining mainly of the beverage glass, it is disadvantageous, that a recess in the joining spot of the flask with the stem is formed, the cleanness of which it is difficult to maintain.
The drawn stem is manufactured by drawing of the stem parison that forms with the flask a compact whole, because it is manufactured together with the flask from the only part of material. The flask is made in such a way that the approximate shape of the flask is manufactured by pressing from the dose of molten glass together with the final shape of the stem parison. Then the flask will be formed-up by blowing to the final required shape. The disadvantage of it is the fact, that for making the flask with the stem parison, sizable automatic pressing and blowing machines are necessary and their price is substantially higher then the price of blowing machines and their operation and maintenance are also more expensive. Also the costs for the manufacturing of glass-blowing moulds needed for the flask rough pressing are very high. In spite of the fact that the final flask shape is being produced in the glass-blowing mould, the surface quality of the flask can be lowered as a result of tool marks during the pressing.
From the commercial point of view, it seems to be perfect to produce flasks of crystal household glass of barium crystal glass with the stem parison on inexpensive automatic glass-blowing machines. But the attempts to produce flasks with the stem parison on usual automatic blowing machine were unsuccessful. As the glass-blowing mould has an aperture on its bottom part, into that the stem parison being in that time in the plastic state, was introduced by the action of its gravity after the filling of the glass-blowing mould cavity with the flask, occurred a sticking of the stem parison and of the outer wall of the flask bottom to the glass-blowing mould. As the blown flask rotates in the glass-blowing mould and the glass-blowing mould is stationary, then a deformation both of the stem parison and the flask bottom occur.